Plastic sack



April 16, 1968 R. w. DlcKsoN PLASTIC SACK Filed Sept. 6, 1966 FIG. l

United States Patent O 3,378,189 l PLASTIC SACK Robert Walker Dickson, Welwyn Garden City, England, assgnor to British Visqueen Limited, London, England Filed Sept. 6, 1966, Ser. No. 577,492

Claims priority, application Great Britain, Sept. 6, 1965,

1 Claim. (Cl. 229-53) ABSTRACT OF THE DISCLOSURE A plastic sack of the type having side gussets infolded Ibetween the sides of the opposed walls of the sack, the sack being adapted to assume a block ended shape when it is lled and closed by a straight seam across its mouth, at least one of the outwardly directed pleats formed by the gussets at each side of the mouth of the sack being provided with a weld of rounded configuration between the gusset and the sack wall facing it.

This invention relates to a gusseted plastic sack.

In closing filled gusseted plastic sacks by bringing the opposite sides of the mouth of the sack together with the gusset portion folded between them, and joining the edges together, usually by heat sealing, it is often difficult to locate the gusset folds in the distended mouth of the sack. This frequently causes delay in the sack closing operation, thus adding to costs.

The present invention provides a means by which the sack closing operation may be facilitated.

The invention provides a plastic sack of the type having side gussets infolded between the sides of the opposed walls of the sack, the sack thus being adapted to assume a `block ended shape when it is filled and closed by a straight seam across its mouth, with the ends of the out wardly directed pleats formed by the gusset and the sack walls providing, at each side of the block end, corners that are normally empty of the sack contents and lie substantially flat against the end of the sack, in which at least one of said outwardly directed pleats at each side of the mouth of the sack is provided with a weld between the gusset and the sack wall facing it, in the portion of the pleat that is destined to form one of said empty corners.

It will be appreciated that although the major portion of the empty corners will normally lie substantially at against the end of the sack, a small portion of the corners will be included in the upstanding seam that Ais formed whentthe mouth ofthe sack is closed. The welds provided in the corner portions in accordance with the invention may be wholly included in this seam, although it is preferred that they extend to, or are =wholly located, below the normal seaming line, since the gusset folds are more clearly located when the weld is well spaced from the top edge of the sack.

Welds may be provided in all four corner portions of the sack mouth, so that all the gusset folds are positively located. However, the provision of only one weld at each side of the mouth of the sack, preferably in adjacent pleats (front or 'back), but alternatively in diagonally opposite pleats, is found to give a great improvement in the ease of closing the sack. Such an arrangement is in fact generally preferred, for it provides the lesser restriction in the width of the sack mouth and thus allows the sack to be more easily filled. It is generally preferred that the arrangement of the welds is not such that all four of the outwardly directed pleats are wholly prevented from opening to contribute to the opening of the sack mouth. However, all four of the pleats may quite satisfactorily be provided with welds that stop short of the inwardly diice rected folds of the gussets, without impossing an undue restriction on the opening of the sack mouth.

In accordance with a further feature of the invention, an air vent comprising a perforation through the sack wall is provided in conjunction,` with at least one of said welds in a corner portion of an outwardly directed pleat, the position of the air vent andthe shape of the weld being such that the weld is adaptedgto screen the air vent from the contents of the sack but to allow the passage of air from the sack interior to the air vent.

One preferred form of the invention will now be more particularly described =by way of example with reference to the accompanying drawingsgsrfin which:

FIGURE 1 is a side view of one side of the gusseted sack provided with a weld in one corner portion; and

FIGURE 2 is a plan of the end of such a sack after it has been filled and sealed.

In these figures: 1

1 and 2 represent the said outwardly directed pleats at one side of the sack; 3 is a Acrescent-shaped weld between the two thicknesses of pleat 1 of the gusset, in the portion destined to form the empty corner AEC, shown in FIG- URE 2, when the sack has been filled and closed; and 4, in FIGURE 2, is the straight seam closing the mouth of the filled sack. 5 shows a position at which an air vent may be provided if desired.

Various modifications may be made in the sack partic ularly described. For example, the weld 31, particularly when no air vent is provided, may follow a straight line or may be a spot weld between the film layers, or more than one weld may be provided. It is preferred, however, that the weld be of a rounded configuration, for example crescent shaped or arc shaped, or substantially semi-circular, since this distributes strains around the weld; considera-ble strains may be imposed upon the weld when the sack is being filled.

The air vent perforation, if provided, need be no larger than a pinhole puncture through the wall of the sack, and this puncture may penetrate both walls of the pleat, so that the corner portion contains two perforations. The fact that the corner portion remains empty of contents, with the Walls of the pleat flattened together, provides that this perforated portion will act as a self closing valve to allow the escape of air from inside the sack Iwhen the pressure therein is above atmospheric pressure, but to be closed by pressure of the atmosphere on the film layers when the inside pressure falls below atmospheric pressure.

As stated hereinbefore, in this embodiment of theA in vention the perforation or perforations are screened from the contents of the sack by the weld between the walls of the pleat on the side of the perforations nearer to the contents of the sack, the weld however leaving an air channel between the said walls from the interior of the sack to the perforation. A crescent shaped, arc shaped, or substantially semicircular weld is again preferred, for the reason that it then more effectively shields the air vent from the contents of the sack.

When a crescent shaped, arc shaped, or substantially semicircular weld is provided to shield the vent in this embodiment of the invention, the distance of the ends of the weld from the edge fold is preferably a maximum consistent with none of the contents of the sack (fertilizer granules, for example) passing into the area containing the vent hole. Generally a separation of from 1A to inch between the ends of the weld and the edge fold gives high security combined with ease of venting.

The sacks of this invention may be used for packing any materials, but are especially useful for packing powdered or granular materials, for example fertilizers, plastic granules, cement, salt, feeding stuffs. Polythene and poly` vinyl chloride heavy duty films are widely used for mak- 3. ing sacks for such applications, and the sacks of this invention may readily be made from these materials' and also from other plastic films, for example from films of other polyolelines, for example polypropylene.

I claim:

1. In a plastic sack of the type having side gussets infolded between the sides of the opposed walls of the sack, the sack thus being adapted to assume a [block ended shape when it is filled and closed by a straight seam across its mouth, with the ends of the outwardly directed pleats formed by the gusset and the sack walls providing, at each side of the block end, corners that are normally empty of the sack contents and lie substantially flat against the end of the sack, the improvement consisting in that at least one of said outwardly directed pleats at each side of the mouth of the sack is provided with a weld of rounded configuration between the gusset and the sack wall facing it, in the portion of `the pleat that is destined to form one of said empty corners, but at least a part of at least one of said outwardly directed pleats at each side of the mouth is left free to open to contribute to the opening of the sack mouth.

References Cited UNITED STATES PATENTS DAVID M. BOCKENEK, Primary Examiner. 

